Treatment of mixed metal oxide catalyst

ABSTRACT

A catalyst comprising a mixed metal oxide is useful for the vapor phase oxidation of an alkane or a mixture of an alkane and an alkene to an unsaturated carboxylic acid and for the vapor phase ammoxidation of an alkane or a mixture of an alkane and an alkene to an unsaturated nitrile. The catalyst is treated with a source of hydrogen, an alcohol, a source of NO x  or a mixture thereof.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This is a non-provisional application of prior U.S. provisionalapplication Ser. No. 60/339,408 filed on Oct. 26, 2001, now abandoned.

The present invention relates to an improved catalyst for the oxidationof alkanes or a mixture of alkanes and alkenes to their correspondingunsaturated carboxylic acids by vapor phase catalytic oxidation; to amethod of making the catalyst; and to a process for the vapor phasecatalytic oxidation of alkanes or a mixture of alkanes and alkenes totheir corresponding unsaturated carboxylic acids. The present inventionalso relates to a method of producing unsaturated nitrites by subjectingalkanes or a mixture of alkanes and alkenes to vapor phase catalyticoxidation in the presence of ammonia.

Nitriles, such as acrylonitrile and methacrylonitrile, have beenindustrially produced as important intermediates for the preparation offibers, synthetic resins, synthetic rubbers, and the like. The mostpopular method for producing such nitrites is to subject an olefin suchas propene or isobutene to a catalytic reaction with ammonia and oxygenin the presence of a catalyst in a gaseous phase at a high temperature.Known catalysts for conducting this reaction include a Mo—Bi—P—Ocatalyst, a V—Sb—O catalyst, an Sb—U—V—Ni—O catalyst, a Sb—Sn—Ocatalyst, a V—Sb—W—P—O catalyst and a catalyst obtained by mechanicallymixing a V—Sb—W—O oxide and a Bi—Ce—Mo—W—O oxide. However, in view ofthe price difference between propane and propene or between isobutaneand isobutene, attention has been drawn to the development of a methodfor producing acrylonitrile or methacrylonitrile by an ammoxidationreaction wherein a lower alkane, such as propane or isobutane, is usedas a starting material, and it is catalytically reacted with ammonia andoxygen in a gaseous phase in the presence of a catalyst.

In particular, U.S. Pat. No. 5,281,745 discloses a method for producingan unsaturated nitrile comprising subjecting an alkane and ammonia inthe gaseous state to catalytic oxidation in the presence of a catalystwhich satisfies the conditions:

(1) the mixed metal oxide catalyst is represented by the empiricalformulaMo_(a)V_(b)Te_(c)X_(x)O_(n)wherein X is at least one element selected from the group consisting ofniobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron and cerium and, when a=1, b=0.01 to1.0, c=0.01 to 1.0, x=0.01 to 1.0 and n is a number such that the totalvalency of the metal elements is satisfied; and

(2) the catalyst has X-ray diffraction peaks at the following angles(±0.3°) of 2θ in its X-ray diffraction pattern: 22.1°, 28.2°, 36.2°,45.2° and 50.0°.

Similarly, Japanese Laid-Open Patent Application Publication No.6-228073 discloses a method of nitrile preparation comprising reactingan alkane in a gas phase contact reaction with ammonia in the presenceof a mixed metal oxide catalyst of the formulaW_(a)V_(b)Te_(c)X_(x)O_(n)wherein X represents one or more elements selected from niobium,tantalum, titanium, aluminum, zirconium, chromium, manganese, iron,ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony,bismuth, indium and cerium and, when a=1, b=0.01 to 1.0, c=0.01 to 1.0,x=0.01 to 1.0 and n is determined by the oxide form of the elements.

U.S. Pat. No. 6,043,185 also discloses a catalyst useful in themanufacture of acrylonitrile or methacrylonitrile by the catalyticreaction in the vapor phase of a paraffin selected from propane andisobutane with molecular oxygen and ammonia by catalytic contact of thereactants in a reaction zone with a catalyst, wherein the catalyst hasthe empirical formulaMo_(a)V_(b)Sb_(c)Ga_(d)X_(e)O_(x)where X is one or more of As, Te, Se, Nb, Ta, W, Ti, Zr, Cr, Mn, Fe, Ru,Co, Rh, Ni, Pd, Pt, B, In, Ce, Re, Ir, Ge, Sn, Bi, Y, Pr, an alkalimetal and an alkaline earth metal; and when a=1, b=0.0 to 0.99, c=0.01to 0.9, d=0.01 to 0.5, e=0.0 to 1.0 and x is determined by the oxidationstate of the cations present.

Unsaturated carboxylic acids such as acrylic acid and methacrylic acidare industrially important as starting materials for various syntheticresins, coating materials and plasticizers. Commercially, the currentprocess for acrylic acid manufacture involves a two-step catalyticoxidation reaction starting with a propene feed. In the first stage,propene is converted to acrolein over a modified bismuth molybdatecatalyst. In the second stage, acrolein product from the first stage isconverted to acrylic acid using a catalyst composed of mainly molybdenumand vanadium oxides. In most cases, the catalyst formulations areproprietary to the catalyst supplier, but the technology is wellestablished. Moreover, there is an incentive to develop a single stepprocess to prepare the unsaturated acid from its corresponding alkene.Therefore, the prior art describes cases where complex metal oxidecatalysts are utilized for the preparation of unsaturated acid from acorresponding alkene in a single step.

European Published Patent Application No. 0 630 879 B1 discloses aprocess for producing an unsaturated aldehyde and a carboxylic acidwhich comprises subjecting propene, isobutene or tertiary butanol to gasphase catalytic oxidation with molecular oxygen in the presence of (i) acatalyst composite oxide represented by the formulaMo_(a)Bi_(b)Fe_(c)A_(d)B_(e)C_(f)D_(g)O_(x)wherein A represents Ni and/or Co, B represents at least one elementselected from Mn, Zn, Ca, Mg, Sn and Pb, C represents at least oneelement selected from P, B, As, Te, W, Sb and Si, and D represents atleast one element selected from K, Rb, Cs and Tl; andwherein,when a=12, 0<b≦10, 0<c≦10, 1≦d≦10, 0≦e≦10, 0≦f≦20 and 0≦g≦2, andx has a value dependent on the oxidation state of the other elements;and (ii) a molybdenum oxide which in itself is substantially inert tosaid gas phase catalytic oxidation to provide the correspondingunsaturated aldehyde and unsaturated carboxylic acid.

Japanese Laid-Open Patent Application Publication No. 07-053448discloses the manufacture of acrylic acid by the gas-phase catalyticoxidation of propene in the presence of mixed metal oxides containingMo, V, Te, O and X wherein X is at least one of Nb, Ta, W, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Li, Na, K, Rb, Cs andCe.

Published International Application No. WO 00/09260 discloses a catalystfor selective oxidation of propene to acrylic acid and acroleincontaining a catalyst composition comprising the elements Mo, V, La, Pd,Nb and X in the following ratio:Mo_(a)V_(b)La_(c)Pd_(d)Nb_(e)X_(f)wherein X is Cu or Cr or a mixture thereof,

-   -   a is 1,    -   b is 0.01 to 0.9,    -   c is >0 to 0.2    -   d is 0.0000001 to 0.2,    -   e is 0 to 0.2, and    -   f is 0 to 0.2; and        wherein the numerical values of a, b, c, d, e and f represent        the relative gram-atom ratios of the elements Mo, V, La, Pd, Nb        and X, respectively, in the catalyst and the elements are        present in combination with oxygen.

Commercial incentives also exist for producing acrylic acid using alower cost propane feed. Therefore, the prior art describes caseswherein a mixed metal oxide catalyst is used to convert propane toacrylic acid in one step.

U.S. Pat. No. 5.380,933 discloses a method for producing an unsaturatedcarboxylic acid comprising subjecting an alkane to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing amixed metal oxide comprising, as essential components, Mo, V, Te, O andX, wherein X is at least one element selected from the group consistingof niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron, indium and cerium; and wherein theproportions of the respective essential components, based on the totalamount of the essential components, exclusive of oxygen, satisfy thefollowing relationships:0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5,wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Teand X, respectively, based on the total amount of the essentialcomponents exclusive of oxygen.

Published International Application No. WO 00/29106 discloses a catalystfor selective oxidation of propane to oxygenated products includingacrylic acid, acrolein and acetic acid, said catalyst system containinga catalyst composition comprisingMo_(a)V_(b)Ga_(c)Pd_(d)Nb_(e)X_(f)wherein X is at least one element selected from La, Te, Ge, Zn, Si, Inand W,

-   -   a is 1,    -   b is 0.01 to 0.9,    -   c is >0 to 0.2,    -   d is 0.0000001 to 0.2,    -   e is >0 to 0.2, and    -   f is 0.0 to 0.5; and        wherein the numerical values of a, b, c, d, e and f represent        the relative gram-atom ratios of the elements Mo, V, Ga, Pd, Nb        and X, respectively, in the catalyst and the elements are        present in combination with oxygen.

Japanese Laid-Open Patent Application Publication No. 2000-037623discloses a method for producing an unsaturated carboxylic acidcomprising subjecting an alkane to a vapor phase catalytic oxidation inthe presence of a catalyst having the empirical formulaMoV_(a)Nb_(b)X_(c)Z_(d)O_(n)wherein X is at least one element selected from the group consisting ofTe and Sb, Z is at least one element selected from the group consistingof W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B,Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earthelements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determinedby the oxidation states of the other elements.

Despite the above-noted attempts to provide new and improved catalystsfor the oxidation of alkanes to unsaturated carboxylic acids and for theammoxidation of alkanes to unsaturated nitrites, one impediment to theprovision of a commercially viable process for such catalytic oxidationsis the identification of a catalyst providing adequate conversion andsuitable selectivity, thereby providing sufficient yield of theunsaturated product. Another limitation to the prior art is lack ofproviding a commercially viable, three dimensional structure onto whichone may support the catalyst or into which one may formulate thecatalyst.

By the present invention, there are provided catalysts wherein theperformance is enhanced by treatment of the catalyst with a gaseoustreatment agent, and more particularly a treatment agent selected fromthe group consisting of hydrogen, alkanols, a source of NO_(x)(particularly a gaseous source) and mixtures thereof.

Thus, in a first aspect, the present invention provides a catalystcomprising a mixed metal oxide having the empirical formulaA_(a)D_(b)E_(c)X_(d)O_(e), wherein A is at least one element selectedfrom the group consisting of Mo and W, D is at least one elementselected from the group consisting of V and Ce, E is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atleast one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na,K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Ag, Pb, P, Pm, Eu, Gd, Dy,Ho, Er, Tm, Yb and Lu; and a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to1.0, and e is dependent on the oxidation state of said other elements.The catalyst composition, during or after calcination, is treated with atreatment agent selected from the group consisting of hydrogen,alcohols, a source of NO_(x) and mixtures thereof.

As will be seen from the discussion herein, preferably the treatmentagent is contacted with the catalyst (which may include precursorsthereof) while the treatment agent is in a liquid or gaseous state.Thus, any of a number of suitable delivery techniques may be employed tobring the treatment agent into contact with the catalyst, includingthose such as gas flow, vapor reflux, saturation, or the like. Thus, theprocess may be performed continuously, in batch or a combinationthereof.

Accordingly, preferred treatment agents may be selected from one or moreof hydrogen, alkanols (such as methanol, ethanol, propanol or higherorder alcohols), diols, or a source of NO_(x) (preferably a gaseoussource) selected from the group consisting of NO, N₂O, NO₂ and mixturesthereof. The treatment agents may be provided in pure form, or they maydiluted or otherwise admixed with other fluid carriers.

Though other crystallographic results are possible, one preferredresulting catalyst exhibits the following five main diffraction peaks atspecific diffraction angles 2θ in the X-ray diffraction pattern of thepromoted mixed metal oxide (as measured using Cu-Kα radiation as thesource):

X-ray lattice plane Diffraction angle 2θ Spacing medium Relative (±0.3°)(Å) intensity 22.1° 4.02 100 28.2° 3.16 20~150 36.2° 2.48 5~60 45.2°2.00 2~40 50.0° 1.82 2~40

The intensity of the X-ray diffraction peaks may vary upon the measuringof each crystal. However, the intensity, relative to the peak intensityat 22.1° being 100, is usually within the above ranges. Generally, thepeak intensities at 2θ=22.1° and 28.2° are distinctly observed.

The present mixed metal oxide can be prepared in a suitable manner suchas that illustrated in the following discussion. Thus, in a first step aslurry or solution may be formed by admixing metal compounds, preferablyat least one of which contains oxygen, and at least one solvent inappropriate amounts to form the slurry or solution. Preferably, asolution is formed at this stage of the catalyst preparation. Generally,the metal compounds contain elements A, D, E, X and O, as previouslydefined.

Suitable solvents include water; alcohols including, but not limited to,methanol, ethanol, propanol, and diols, etc.; as well as other polarsolvents known in the art. Generally, water is preferred. The water isany water suitable for use in chemical syntheses including, withoutlimitation, distilled water and de-ionized water. The amount of waterpresent is preferably an amount sufficient to keep the elementssubstantially in solution long enough to avoid or minimize compositionaland/or phase segregation during the preparation steps. Accordingly, theamount of water will vary according to the amounts and solubilities ofthe materials combined. However, as stated above, the amount of water ispreferably sufficient to ensure an aqueous solution is formed, and not aslurry, at the time of mixing.

For example, when a mixed metal oxide of the formulaMo_(a)V_(b)Te_(c)Nb_(d)O_(e) wherein the element A is Mo, the element Mis V, the element N is Te and the element X is Nb, is to be prepared, anaqueous solution of niobium oxalate may be added to an aqueous solutionor slurry of ammonium heptamolybdate, ammonium metavanadate and telluricacid, so that the atomic ratio of the respective metal elements would bein the prescribed proportions.

Once the aqueous slurry or solution (preferably a solution) is formed,the water is removed by any suitable method, known in the art, to form acatalyst precursor. Such methods include, without limitation, vacuumdrying, freeze drying, spray drying, rotary evaporation and air drying.Vacuum drying is generally performed at pressures ranging from 10 mmHgto 500 mmHg. Freeze drying typically entails freezing the slurry orsolution, using, for instance, liquid nitrogen, and drying the frozenslurry or solution under vacuum. Spray drying is generally performedunder an inert atmosphere such as nitrogen or argon, with an inlettemperature ranging from 125° C. to 200° C. and an outlet temperatureranging from 75° C. to 150° C. Rotary evaporation is generally performedat a bath temperature of from 25° C. to 90° C. and at a pressure of from10 mmHg to 760 mmHg, preferably at a bath temperature of from 40° to 90°C. and at a pressure of from 10 mmHg to 350 mmHg, more preferably at abath temperature of from 40° C. to 60° C. and at a pressure of from 10mmHg to 40 mmHg. Air drying may be effected at temperatures ranging from25° C. to 90° C. Rotary evaporation or air drying are generallypreferred.

Once obtained, the catalyst precursor is calcined. The calcination maybe conducted in an oxygen-containing atmosphere or in the substantialabsence of oxygen, e.g., in an inert atmosphere or in vacuo. The inertatmosphere may be any material which is substantially inert, i.e., doesnot react or interact with, the catalyst precursor. Suitable examplesinclude, without limitation, nitrogen, argon, xenon, helium or mixturesthereof. Preferably, the inert atmosphere is argon or nitrogen, morepreferably argon. The inert atmosphere may flow over the surface of thecatalyst precursor or may not flow thereover (a static environment).When the inert atmosphere does flow over the surface of the catalystprecursor, the flow rate can vary over a wide range, e.g., at a spacevelocity of from 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In a preferred mode of operation, the catalyst precursor is calcined intwo stages. In the first stage, the catalyst precursor is calcined in anoxidizing environment (e.g. air) at a temperature of from 275° C. to400° C., preferably from 275° C. to 325° C. for from 15 minutes to 8hours, preferably for from 1 to 3 hours. In the second stage, thematerial from the first stage is calcined in a non-oxidizing environment(e.g., an inert atmosphere) at a temperature of from 500° C. to 700° C.,preferably for from 550° C. to 650° C., for 15 minutes to 8 hours,preferably for from 1 to 3 hours. Optionally, a reducing gas, such as,for example, ammonia or hydrogen, may be added during the second stagecalcination.

In a particularly preferred mode of operation, the catalyst precursor inthe first stage is placed in the desired oxidizing atmosphere at roomtemperature and then raised to the first stage calcination temperatureand held there for the desired first stage calcination time. Theatmosphere is then replaced with the desired non-oxidizing atmospherefor the second stage calcination, the temperature is raised to thedesired second stage calcination temperature and held there for thedesired second stage calcination time.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

With calcination, a catalyst is formed having the formulaA_(a)D_(b)E_(c)X_(d)O_(e f) wherein A, D, E, X, O, a, b, c, d and e areas previously defined.

The starting materials for the above promoted mixed metal oxide are notlimited to those described above. A wide range of materials including,for example, oxides, nitrates, halides or oxyhalides, alkoxides,acetylacetonates, and organometallic compounds may be used. For example,ammonium heptamolybdate may be utilized for the source of molybdenum inthe catalyst. However, compounds such as MoO₃, MoO₂, MoCl₅, MoOCl₄,Mo(OC₂H₅)₅, molybdenum acetylacetonate, phosphomolybdic acid andsilicomolybdic acid may also be utilized instead of ammoniumheptamolybdate. Similarly, ammonium metavanadate may be utilized for thesource of vanadium in the catalyst. However, compounds such as V₂O₅,V₂O₃, VOCl₃, VCl₄, VO(OC₂H₅)₃, vanadium acetylacetonate and vanadylacetylacetonate may also be utilized instead of ammonium metavanadate.The tellurium source may include telluric acid, TeCl₄, Te(OC₂H₅)₅,Te(OCH(CH₃)₂)₄ and TeO₂. The niobium source may include ammonium niobiumoxalate, Nb₂O₅, NbCl₅, niobic acid or Nb(OC₂H₅)₅ as well as the moreconventional niobium oxalate.

The catalyst composition, during or after calcination, is treated withthe treatment agent, by contacting the catalyst precursors and/or thecatalyst, respectively, with a treatment agent selected from the groupconsisting of hydrogen, alcohols, a source of NO_(x) (preferably agaseous source) and mixtures thereof. It will be appreciated thatadditionally, or alternatively, the treatment agent may be added to thereaction feed composition. Treatment may take place below, at or aboveroom temperature. In elevated temperature treatments, for instance, thetreatment agent may be contacted with the catalyst at one or moretemperatures greater than 50° C., greater than 100° C., or even greaterthan 200° C., such as during a calcination step. The amount of time thecatalyst is contacted with the treatment agent may vary from as low as afew seconds, to 4 or more hours. The catalyst may be contacted fortreating all or a portion of it. In instances where the treatment agentis flowed over or relative to a catalyst, the flow rate may vary asdesired, such as on the order of 1 cc/mm, 10 cc/mm, 100 cc/mm or evenhigher.

A treated mixed metal oxide, thus obtained, exhibits excellent catalyticactivities by itself. However, the mixed metal oxide can be converted toa catalyst having higher activities by grinding.

There is no particular restriction as to the grinding method, andconventional methods may be employed. As a dry grinding method, a methodof using a gas stream grinder may, for example, be mentioned whereincoarse particles are permitted to collide with one another in a highspeed gas stream for grinding. The grinding may be conducted not onlymechanically but also by using a mortar or the like in the case of asmall scale operation.

As a wet grinding method wherein grinding is conducted in a wet state byadding water or an organic solvent to the above mixed metal oxide, aconventional method of using a rotary cylinder-type medium mill or amedium-stirring type mill, may be mentioned. The rotary cylinder-typemedium mill is a wet mill of the type wherein a container for the objectto be ground is rotated, and it includes, for example, a ball mill and arod mill. The medium-stirring type mill is a wet mill of the typewherein the object to be ground, contained in a container is stirred bya stirring apparatus, and it includes, for example, a rotary screw typemill, and a rotary disc type mill.

The conditions for grinding may suitably be set to meet the nature ofthe above-mentioned promoted mixed metal oxide, the viscosity, theconcentration, etc. of the solvent used in the case of wet grinding, orthe optimum conditions of the grinding apparatus. However, it ispreferred that grinding is conducted until the average particle size ofthe ground catalyst precursor would usually be at most 20 μm, morepreferably at most 5 μm. Improvement in the catalytic performance mayoccur due to such grinding.

Further, in some cases, it is possible to further improve the catalyticactivities by further adding a solvent to the ground catalyst precursorto form a solution or slurry, followed by drying again. There is noparticular restriction as to the concentration of the solution orslurry, and it is usual to adjust the solution or slurry so that thetotal amount of the starting material compounds for the ground catalystprecursor is from 10 to 60 wt %. Then, this solution or slurry is driedby a method such as spray drying, freeze drying, evaporation to drynessor vacuum drying, preferably by the spray drying method. Further,similar drying may be conducted also in the case where wet grinding isconducted.

The oxide obtained by the above-mentioned method may be used as a finalcatalyst, but it may further be subjected to heat treatment usually at atemperature of from 200° to 700° C. for from 0.1 to 10 hours.

The present invention also provides a process for producing anunsaturated carboxylic acid, which comprises subjecting an alkane, or amixture of an alkane and an alkene, to a vapor phase catalytic oxidationreaction in the presence of a catalyst containing the above treatedmixed metal oxide, to produce an unsaturated carboxylic acid.

In the production of such an unsaturated carboxylic acid, it ispreferred to employ a starting material gas that contains steam. In sucha case, as a starting material gas to be supplied to the reactionsystem, a gas mixture comprising a steam-containing alkane, or asteam-containing mixture of alkane and alkene, and an oxygen-containinggas, is usually used. However, the steam-containing alkane, or thesteam-containing mixture of alkane and alkene, and the oxygen-containinggas may be alternately supplied to the reaction system. The steam to beemployed may be present in the form of steam gas in the reaction system,and the manner of its introduction is not particularly limited.

Further, as a diluting gas, an inert gas such as nitrogen, argon orhelium may be supplied. The molar ratio (alkane or mixture of alkane andalkene):(oxygen):(diluting gas):(H₂O) in the starting material gas ispreferably (1):(0.1 to 10):(0 to 20):(0.2 to 70), more preferably (1):(1to 5.0):(0 to 10):(5 to 40).

When steam is supplied together with the alkane, or the mixture ofalkane and alkene, as starting material gas, the selectivity for anunsaturated carboxylic acid is distinctly improved, and the unsaturatedcarboxylic acid can be obtained from the alkane, or mixture of alkaneand alkene, in good yield simply by contacting in one stage. However,the conventional technique utilizes a diluting gas such as nitrogen,argon or helium for the purpose of diluting the starting material. Assuch a diluting gas, to adjust the space velocity, the oxygen partialpressure and the steam partial pressure, an inert gas such as nitrogen,argon or helium may be used together with the steam.

As the starting material alkane it is preferred to employ a C₃₋₈alkane,particularly propane, isobutane or n-butane; more preferably, propane orisobutane; most preferably, propane. According to the present invention,from such an alkane, an unsaturated carboxylic acid such as anα,β-unsaturated carboxylic acid can be obtained in good yield. Forexample, when propane or isobutane is used as the starting materialalkane, acrylic acid or methacrylic acid will be obtained, respectively,in good yield.

In the present invention, as the starting material mixture of alkane andalkene, it is preferred to employ a mixture of C₃₋₈alkane andC₃₋₈alkene, particularly propane and propene, isobutane and isobutene orn-butane and n-butene. As the starting material mixture of alkane andalkene, propane and propene or isobutane and isobutene are morepreferred. Most preferred is a mixture of propane and propene. Accordingto the present invention, from such a mixture of an alkane and analkene, an unsaturated carboxylic acid such as an α,β-unsaturatedcarboxylic acid can be obtained in good yield. For example, when propaneand propene or isobutane and isobutene are used as the starting materialmixture of alkane and alkene, acrylic acid or methacrylic acid will beobtained, respectively, in good yield. Preferably, in the mixture ofalkane and alkene, the alkene is present in an amount of at least 0.5%by weight, more preferably at least 1.0% by weight to 95% by weight;most preferably, 3% by weight to 90% by weight.

As an alternative, an alkanol, such as isobutanol, which will dehydrateunder the reaction conditions to form its corresponding alkene, i.e.isobutene, may also be used as a feed to the present process or inconjunction with the previously mentioned feed streams.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower, alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the oxidation reaction of the presentinvention is not clearly understood, but the oxidation reaction iscarried out by oxygen atoms present in the above mixed metal oxide or bymolecular oxygen present in the feed gas. To incorporate molecularoxygen into the feed gas, such molecular oxygen may be pure oxygen gas.However, it is usually more economical to use an oxygen-containing gassuch as air, since purity is not particularly required.

It is also possible to use only an alkane, or a mixture of alkane andalkene, substantially in the absence of molecular oxygen for the vaporphase catalytic reaction. In such a case, it is preferred to adopt amethod wherein a part of the catalyst is appropriately withdrawn fromthe reaction zone from time to time, then sent to an oxidationregenerator, regenerated and then returned to the reaction zone forreuse. As the regeneration method of the catalyst, a method may, forexample, be mentioned which comprises contacting an oxidative gas suchas oxygen, air or nitrogen monoxide with the catalyst in the regeneratorusually at a temperature of from 300° to 600° C.

A process for producing an unsaturated carboxylic acid may also beemployed where propane is used as the starting material alkane, and airis used as the oxygen source. In such an instance, the reaction systemmay be preferably a fixed bed system. The proportion of air to besupplied to the reaction system is important for the selectivity for theresulting acrylic acid, and it is usually at most 25 moles, preferablyfrom 0.2 to 18 moles per mole of propane, whereby high selectivity foracrylic acid can be obtained. This reaction can be conducted usuallyunder atmospheric pressure, but may be conducted under a slightlyelevated pressure or slightly reduced pressure. With respect to otheralkanes such as isobutane, or to mixtures of alkanes and alkenes such aspropane and propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

Typical reaction conditions for the oxidation of propane or isobutane toacrylic acid or methacrylic acid may be utilized in the practice of thepresent invention. The process may be practiced in a single pass mode(only fresh feed is fed to the reactor) or in a recycle mode (at least aportion of the reactor effluent is returned to the reactor). Generalconditions for the process of the present invention are as follows: thereaction temperature can vary from 200° C. to 700° C., but is usually inthe range of from 200° C. to 550° C., more preferably 250° C. to 480°C., most preferably 300° C. to 400° C.; the gas space velocity, SV, inthe vapor phase reaction is usually within a range of from 100 to 10,000hr⁻¹, preferably 300 to 6,000 hr⁻¹, more preferably 300 to 2,000 hr⁻¹;the average contact time with the catalyst can be from 0.01 to 10seconds or more, but is usually in the range of from 0.1 to 10 seconds,preferably from 0.2 to 6 seconds; the pressure in the reaction zoneusually ranges from 0 to 75 psig, but is preferably no more than 50psig. In a single pass mode process, it is preferred that the oxygen besupplied from an oxygen-containing gas such as air. The single pass modeprocess may also be practiced with oxygen addition. In the practice ofthe recycle mode process, oxygen gas by itself is the preferred sourceso as to avoid the build up of inert gases in the reaction zone.

Of course, in the oxidation reaction of the present invention, it isimportant that the hydrocarbon and oxygen concentrations in the feedgases be maintained at the appropriate levels to minimize or avoidentering a flammable regime within the reaction zone or especially atthe outlet of the reactor zone. Generally, it is preferred that theoutlet oxygen levels be low to both minimize after-burning and,particularly, in the recycle mode of operation, to minimize the amountof oxygen in the recycled gaseous effluent stream. In addition,operation of the reaction at a low temperature (below 450° C.) isextremely attractive because after-burning becomes less of a problem,which enables the attainment of higher selectivity to the desiredproducts. The catalyst of the present invention operates moreefficiently at the lower temperature range set forth above,significantly reducing the formation of acetic acid and carbon oxides,and increasing selectivity to acrylic acid. As a diluting gas to adjustthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium may be employed.

When the oxidation reaction of propane, and especially the oxidationreaction of propane and propene, is conducted by the method of thepresent invention, carbon monoxide, carbon dioxide, acetic acid, etc.may be produced as by-products, in addition to acrylic acid. Further, inthe method of the present invention, an unsaturated aldehyde maysometimes be formed depending upon the reaction conditions. For example,when propane is present in the starting material mixture, acrolein maybe formed; and when isobutane is present in the starting materialmixture, methacrolein may be formed. In such a case, such an unsaturatedaldehyde can be converted to the desired unsaturated carboxylic acid bysubjecting it again to the vapor phase catalytic oxidation with thepromoted mixed metal oxide-containing catalyst of the present inventionor by subjecting it to a vapor phase catalytic oxidation reaction with aconventional oxidation reaction catalyst for an unsaturated aldehyde.

In yet another aspect, the method of the present invention comprisessubjecting an alkane, or a mixture of an alkane and an alkene, to avapor phase catalytic oxidation reaction with ammonia in the presence ofa catalyst containing the above treated mixed metal oxide, to produce anunsaturated nitrile.

In the production of such an unsaturated nitrile, as the startingmaterial alkane, it is preferred to employ a C₃₋₈alkane such as propane,butane, isobutane, pentane, hexane and heptane. However, in view of theindustrial application of nitrites to be produced, it is preferred toemploy a lower alkane having 3 or 4 carbon atoms, particularly propaneand isobutane.

Similarly, as the starting material mixture of alkane and alkene, it ispreferred to employ a mixture of C₃₋₈alkane and C₃₋₈alkene such aspropane and propene, butane and butene, isobutane and isobutene, pentaneand pentene, hexane and hexene, and heptane and heptene. However, inview of the industrial application of nitrites to be produced, it ismore preferred to employ a mixture of a lower alkane having 3 or 4carbon atoms and a lower alkene having 3 or 4 carbon atoms, particularlypropane and propene or isobutane and isobutene. Preferably, in themixture of alkane and alkene, the alkene is present in an amount of atleast 0.5% by weight, more preferably at least 1.0% by weight to 95% byweight, most preferably 3% by weight to 90% by weight.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the ammoxidation reaction of this aspect ofthe present invention is not clearly understood. However, the oxidationreaction is conducted by the oxygen atoms present in the above promotedmixed metal oxide or by the molecular oxygen in the feed gas. Whenmolecular oxygen is incorporated in the feed gas, the oxygen may be pureoxygen gas. However, since high purity is not required, it is usuallyeconomical to use an oxygen-containing gas such as air.

As the feed gas, it is possible to use a gas mixture comprising analkane, or a mixture of an alkane and an alkene, ammonia and anoxygen-containing gas, However, a gas mixture comprising an alkane or amixture of an alkane and an alkene and ammonia, and an oxygen-containinggas may be supplied alternately.

When the gas phase catalytic reaction is conducted using an alkane, or amixture of an alkane and an alkene, and ammonia substantially free frommolecular oxygen, as the feed gas, it is advisable to employ a methodwherein a part of the catalyst is periodically withdrawn and sent to anoxidation regenerator for regeneration, and the regenerated catalyst isreturned to the reaction zone. As a method for regenerating thecatalyst, a method may be mentioned wherein an oxidizing gas such asoxygen, air or nitrogen monoxide is permitted to flow through thecatalyst in the regenerator usually at a temperature of from 300° C. to600° C.

A process may also be employed where propane is used as the startingmaterial alkane, and air is used as the oxygen source. The proportion ofair to be supplied for the reaction is important with respect to theselectivity for the resulting acrylonitrile. Namely, high selectivityfor acrylonitrile is obtained when air is supplied within a range of atmost 25 moles, particularly 1 to 15 moles, per mole of the propane. Theproportion of ammonia to be supplied for the reaction is preferablywithin a range of from 0.2 to 5 moles, particularly from 0.5 to 3 moles,per mole of propane. This reaction may usually be conducted underatmospheric pressure, but may be conducted under a slightly increasedpressure or a slightly reduced pressure. With respect to other alkanessuch as isobutane, or to mixtures of alkanes and alkenes such as propaneand propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

The process of the third aspect of the present invention may beconducted at a temperature of, for example, from 250° C. to 480° C. Morepreferably, the temperature is from 300° C. to 400° C. The gas spacevelocity, SV, in the gas phase reaction is usually within the range offrom 100 to 10,000 hr⁻¹, preferably from 300 to 6,000 hr⁻¹, morepreferably from 300 to 2,000 hr⁻¹. As a diluent gas, for adjusting thespace velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium can be employed. When ammoxidation of propaneis conducted by the method of the present invention, in addition toacrylonitrile, carbon monoxide, carbon dioxide, acetonitrile,hydrocyanic acid and acrolein may form as by-products.

The examples set forth below are for illustrative purposes only andshould not be considered as limiting the scope of the invention.

EXAMPLES Example 1–5

In a flask containing 390 g of water, 46.4 g of ammonium heptamolybdatetetrahydrate (Aldrich Chemical Company), 9.2 g of ammonium metavanadate(Alfa-Aesar) and 13.9 g of telluric acid (Aldrich Chemical Company) weredissolved upon heating to 80° C. After cooling to 20° C., 201.3 g of anaqueous solution of niobium oxalate (Reference Metals Company)containing 10.44 mmole/g of niobium was mixed to obtain a solution. Thewater of this solution was removed via a rotary evaporator with a warmwater bath at 50° C. and 28 mm/Hg to obtain 73 g of precursor solid. 25g of the catalyst precursor solid was calcined in a quartz tube byflowing argon, at 600° C. for 2 hours. The oven had previously beenheated to 275° C. and held for one hour, then ramped to 600° C. The flowrate of Ar was set at 100 cc/min. The catalyst thus obtained was pressedin a mold and then broken and sieved to 10–20 mesh granules.Approximately 0.5 g of the granules were packed into a quartz tubereactor for gas phase propane oxidation. The oxidation was conductedwith a feed ratio of propane/steam/air/ of 1/3/96. The effluent from thereactor was analyzed by infrared spectrometry (IR) to determine thepropane conversion and for the yield of acrylic acid. The results areshown in Table 1, with varying oxidation reaction temperatures asbetween the different samples.

TABLE 1 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 1 3 280 12.1 44.8 5.4 2 3 330 33.2 41.613.8 3 3 350 46.0 32.6 15.0 4 3 370 59.3 20.9 12.4 5 3 380 65.9 16.210.7

Examples 6–10

The catalyst prepared in example 1 was calcined in 4% hydrogen (96% N₂)at 280° C. Approximately 0.5 g of the granules were packed into a quartztube reactor for gas phase propane oxidation. The oxidation wasconducted with a feed ratio of propane/steam/air/ of 1/3/96. Theeffluent from the reactor was analyzed by infrared spectrometry (IR) todetermine the propane conversion and for the yield of acrylic acid. Theresults at the respective different oxidation reaction temperatures areshown in Table 2.

TABLE 2 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 6 3 280 10.8 61.9 6.7 7 3 330 30.8 54.716.9 8 3 350 43.5 38.8 16.9 9 3 370 55.9 23.0 12.9 10 3 380 62.1 17.210.7

Examples 11–15

The catalyst prepared in example 1 was calcined in 4% hydrogen (96% N₂)at 325° C. Approximately 0.5 g of the granules were packed into a quartztube reactor for gas phase propane oxidation. The oxidation wasconducted with a feed ratio of propane/steam/air/ of 1/3/96. Theeffluent from the reactor was analyzed by infrared spectrometry (IR) todetermine the propane conversion and for the yield of acrylic acid. Theresults at the respective different oxidation reaction temperatures areshown in Table 3.

TABLE 3 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 11 3 280 11.9 84.3 10.0 12 3 330 31.1 72.522.6 13 3 350 42.8 49.0 21.0 14 3 370 55.9 24.5 13.7 15 3 380 61.6 15.99.8

Examples 16–20

The catalyst prepared in example 1 was calcined in 4% hydrogen (96% N₂)at 400° C. Approximately 0.5 g of the granules were packed into a quartztube reactor for gas phase propane oxidation. The oxidation wasconducted with a feed ratio of propane/steam/air/ of 1/3/96. Theeffluent from the reactor was analyzed by infrared spectrometry (IR) todetermine the propane conversion and for the yield of acrylic acid. Theresults at the respective different oxidation reaction temperatures areshown in Table 4.

TABLE 4 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 16 3 280 10.0 74.0 7.4 17 3 330 28.6 62.617.9 18 3 350 39.5 56.4 22.3 19 3 370 53.5 34.4 18.4 20 3 380 58.8 24.014.1

Example 21–25

A catalyst was prepared using stock metal solutions where solution 1contained Mo, V and Te in the correct ratios and solution 2 contained Nband oxalic acid in the right proportions. The catalyst was made bymixing solution 1 and solution 2. The water of this solution was removedvia a rotary evaporator with a m water bath at 50° C. and 28 mm/Hg toobtain the precursor solid. This catalyst precursor solid was calcinedin a quartz tube by flowing argon, at 600° C. for 2 hours. The oven hadpreviously been heated to 275° C. and held for one hour, then ramped to600° C. The flow rate of Ar was set at 100 cc/min. The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules. Approximately 0.5 g of the granules were packed into a quartztube reactor for gas phase propane oxidation. The oxidation wasconducted with a feed ratio of propane/steam/air/ of 1/3/96. Theeffluent from the reactor was analyzed by infrared spectrometry (IR) todetermine the propane conversion and for the yield of acrylic acid. Theresults at the respective different oxidation reaction temperatures areshown in Table 5.

TABLE 5 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 21 3 360 8.0 50.0 4.0 22 3 370 11.0 45.05.0 23 3 380 13.0 54.0 7.0 24 3 390 16.0 50.0 8.0 25 3 400 19.0 42.0 8.0

Example 26–31

Approximately 10 g of the multi metal oxide catalyst used in example 21was refluxed in 100 cc methanol for 1.5 hour. The methanol wassubsequently removed via a rotary evaporator with a warm water bath at50° C. and 28 mm/Hg to obtain the solid catalyst. This was then dried ina vacuum oven for 72 hours. The catalyst thus obtained was pressed in amold and then broken and sieved to 10–20 mesh granules. Approximately0.5 g of the granules were packed into a quartz tube reactor for gasphase propane oxidation. The oxidation was conducted with a feed ratioof propane/steam/air/ of 1/3/96. The effluent from the reactor wasanalyzed by infrared spectrometry (IR) to determine the propaneconversion and for the yield of acrylic acid. The results at therespective different oxidation reaction temperatures are shown in Table6.

TABLE 6 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 26 3 350 9.0 56.0 5.0 27 3 360 11.0 64.07.0 28 3 370 15.0 60.0 9.0 29 3 380 19.0 58.0 11.0 30 3 390 22.0 50.011.0 31 3 400 26.0 44.0 12.0

Examples 32–34

A catalyst was prepared using stock metal solutions where solution 1contained Mo, V and Te in the correct ratios and solution 2 contained Nband oxalic acid in the right proportions. The catalyst was made bymixing solution 1 and solution 2. The water of this solution was removedvia a rotary evaporator with a warm water bath at 50° C. and 28 mm/Hg toobtain the precursor solid. This catalyst precursor solid was calcinedin a quartz tube by flowing argon, at 600° C. for 2 hours. The oven hadpreviously been heated to 275° C. and held for one hour, then ramped to600° C. The flow rate of Ar was set at 100 cc/min. The catalyst thusobtained was pressed in a mold and then broken and sieved to 10–20 meshgranules. Approx. 0.6 g of the granules were packed into a quartz tubereactor for gas phase propane oxidation. The oxidation was conductedwith a feed ratio of propane/steam/air/of 1/3/96. The effluent from thereactor was analyzed by infra red spectrometry (IR) to determine thepropane conversion and for the yield of acrylic acid. The results at therespective different oxidation reaction temperatures are shown in Table7.

TABLE 7 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 32 3 340 47.6 52.5 25.0 33 3 350 53.6 40.721.8 34 3 370 64.6 18.6 12.0

Example 35–37

A fresh charge of approximately 0.6 g of the catalyst granules used inexample 32 was packed into a quartz tube reactor and treated at 800° C.with a nitrogen gas stream (12.5 cc/min flow rate) containing 14%methanol for 30 min. Nitrogen with no added methanol (12.5/min flowrate) was then passed over the catalyst bed at 400° C. for 30 min.before lowering the catalyst bed to 330° C. while continuing to flownitrogen (12.5/min flow rate). The oxidation was conducted with a feedratio of propane/steam/air of 1/3/96. The effluent from the reactor wasanalyzed by infrared spectrometry (IR) to determine the propaneconversion and for the yield of acrylic acid. The results are shown inTable 8. XRD analysis, before and after methanol treatment, of thecatalyst indicated no phase changes had occurred.

TABLE 8 Residence Temperature % C₃ % AA % AA Example # Time (sec) (° C.)Conversion Selectivity Yield 35 3 340 44.3 64.5 28.6 36 3 350 49.1 52.325.7 37 3 370 63.2 26.0 16.5

Examples 38–39 Example 38

Approximately 100 mL of an aqueous solution containing ammoniumheptamolybdate tetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V)and telluric acid (0.23 Te), formed by dissolving the correspondingsalts in water at 70° C., was added to a 1000 mL rotavap flask. Then 50mL of an aqueous solution of niobium oxalate (0.16M Nb) and oxalic acid(0.58M) were added thereto. After removing the water via a rotaryevaporator with a warm water bath at 50° C. and 28 mm/Hg, the solidmaterials were further dried in a vacuum oven at 25° C. overnight andthen calcined. Calcination was effected by placing the solid materialsin an air atmosphere and then heating them to 275° C. at 10° C./min andholding them under the air atmosphere at 275° C. for one hour; theatmosphere was then changed to argon and the material was heated from275° C. to 600° C. at 2° C./min and the material was held under theargon atmosphere at 600° C. for two hours. The final catalyst had anominal composition of Mo₁V_(0.3)Te_(0.23) Nb_(0.08)O_(f). The catalyst,thus obtained, was pressed in a mold and then broken and sieved to 10–20mesh granules for evaluation.

Example 39

Approximately 6 grams of catalysts from example 1 were ground and placedin a quartz tube and were held in position with quartz wool atapproximately mid-length in the tube. Argon gas (100 mL/min) flows firstthrough a saturator containing 30% aqueous HNO₃ at 40° C. and thenthrough the catalyst in the quartz tube. The catalysts were held at 25°C. for 4 hours to saturate with HNO₃, then heated to 600° C. at 10°C./min and held at 600° C. for 2 hours. The catalyst, thus treated, waspressed in a mold and then broken and sieved to 10–20 mesh granules forreactor evaluation.

Catalysts were evaluated in a 10 cm long Pyrex tube reactor (internaldiameter: 3.9 mm). The catalyst bed (4 cm long) was positioned withglass wool at approximately mid-length in the reactor and was heatedwith an electric furnace. Mass flow controllers and meters regulated thegas flow rate. The oxidation was conducted using a feed gas stream ofpropane, steam and air, with a feed ratio of propane:steam:air of1:3:96. The reactor effluent was analyzed by an FTIR.

The results at 390° C. and at a 3 second residence time are shown inTable 9.

TABLE 9 Residence % C₃ Example Temp. C. Time (sec) Conversion % AA yield38 390 3 41 17 39 390 3 51 26

While the invention has been described in conjunction with the specificembodiments set forth above, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alterations, modifications and variations as fallwithin the spirit and broad scope of the appended claims.

1. A process for improving the performance characteristics of acatalyst, comprising the steps of: a) providing precursors for a mixedmetal oxide having the empirical formulaA_(a)D_(b)E_(c)X_(d)O_(e),  wherein A is at least one element selectedfrom the group consisting of Mo and W, D is at least one elementselected from the group consisting of V and Ce, E is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atleast one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na,K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Ag, Pb, P, Pm, Eu, Gd, Dy,Ho, Er, Tm, Yb and Lu; and a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to1.0, and e is dependent on the oxidation state of said other elements;b) calcining an admixture of said precursors; and c) contacting, noearlier than during said calcining step (b), said precursors with atreatment agent selected from the group consisting of hydrogen, agaseous source of NO_(x) and mixtures thereof.
 2. The process accordingto claim 1, wherein said treatment agent is hydrogen.
 3. The processaccording to claim 1, wherein said treatment agent is a gaseous sourceof NO_(x) selected from the group consisting of NO, N₂O, NO₂ andmixtures thereof.
 4. A catalytic process, comprising the steps of: a)providing precursors for a mixed metal oxide having the empiricalformulaA_(a)D_(b)E_(c)X_(d)O_(e),  wherein A is at least one element selectedfrom the group consisting of Mo and W, D is at least one elementselected from the group consisting of V and Ce, E is at least oneelement selected from the group consisting of Te, Sb and Se, and X is atleast one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na,K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Ag, Pb, P, Pm, Eu, Gd, Dy,Ho, Er, Tm, Yb and Lu; and a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to1.0, and e is dependent on the oxidation state of said other elements;b) calcining an admixture of said precursors; c) contacting, no earlierthan said calcining step (b), said precursors with a treatment agentselected from the group consisting of hydrogen, gaseous NO, gaseous N₂O,gaseous NO₂ and mixtures thereof; and d) subjecting a feed including analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of said catalyst.
 5. Theprocess according to claim 4, wherein said feed of said subjecting step(d) further includes ammonia.